The objectives of this project are the description and measurement of changes that occur in behavior and neuroendocrine physiology during the aging process. Particular emphasis is placed on the use of male and female sexual behavior as dependent variables. Additional behaviors to be studied include operant behavior and open field behavior. The experimental methodologies used will include neonatal hormone administration, central nervous system lesions and administration of neuropharmacological substances. Particular attention will be paid to variables which influence or interact with the aging process as measured by behavioral and neuroendocrine changes.